The prostate is a walnut-shaped gland that produces the milky-white fluid that is part of semen. It is located in front of the rectum and right below the bladder. It is not known exactly why, but the prostate grows larger as a man grows older. This condition is called benign prostatic hyperplasia (BPH), or more simply, an enlarged prostate. The urethra, the tube that carries urine out from the bladder, runs through the prostate (see figure). As the gland enlarges, it can pinch or close off the urethra, making urination difficult or impossible. Even a slightly enlarged prostate can cause trouble.